Physical quantity measuring devices include pressure sensors for measuring pressure. An example of pressure sensors is a strain gauge pressure sensor including: a diaphragm displaceable by a pressure of an introduced fluid to be measured; a cylindrical portion integral with the diaphragm; and a detector provided to a surface of the diaphragm opposite to a surface of the diaphragm that is to be in contact with the fluid to be measured, the detector detecting a displacement of the diaphragm.
A typical example of the strain gauge pressure sensor includes: a pressure-sensitive element; a strain gauge resistance provided to the pressure-sensitive element; a flexible circuit board connecting the pressure-sensitive element and an output terminal; an ASIC (an electronic component) mounted on the flexible circuit board; and a connector attached to an end of the sensor (Patent Literature 1: JP-A-2006-78379).
Another typical example of pressure sensors different from the strain gauge type is an electrostatic capacitive pressure sensor including: a capacitive pressure-sensitive element including a diaphragm; a housing for housing the capacitive pressure-sensitive element; and a conditional electronic circuit provided on the capacitive pressure-sensitive element (Patent Literature 2: JP-A-2011-257393).
In the typical example of Patent Literature 2, the pressure-sensitive element also includes a ceramic base where the diaphragm, which is displaceable by a pressure of a fluid to be measured, is provided. The conditional electronic circuit is provided to a surface of the ceramic base opposite to the surface where the diaphragm is provided. The conditional electronic circuit is electrically connected to a sensing device terminal housed in a connector housing.
Another typical example of pressure sensors different from the strain gauge type is an electrostatic capacitive pressure sensor including a housing and a variable capacitor housed in the housing (Patent Literature 3: JP-A-11-94668).
In the typical example of Patent Literature 3, the variable capacitor includes: a rigid substrate housed in the housing; a flexible diaphragm provided to the substrate; and a signal conditioning circuit provided to the substrate. The housing is provided with a connector. The connector is attached with a connector terminal, which is electrically connected to the signal conditioning circuit.
The strain gauge pressure sensor requires that an electronic component such as an ASIC should be mounted not to interfere with the diaphragm. Therefore, a position where the electronic component is mountable is limited, so that the electronic component is attached to the flexible board in the typical example of Patent Literature 1. In order to attach the electronic component to the flexible board, the flexible board has to be fixed. Attachment of the electronic component to the flexible circuit board thus requires a complicated process. Further, the flexible board needs to be electrically connected to the pressure-sensitive element with the electronic component attached to the flexible board, which results in lowering the efficiency of an assembly process of the pressure sensor and increasing production costs.
In mounting the electronic component, the typical examples of Patent Literatures 2 and 3, which are the electrostatic capacitive type, are free from the above problem unique to the strain gauge type.
Specifically, in the typical example of Patent Literature 2, the conditional electronic circuit is provided to the surface of the pressure-sensitive element opposite to the surface where the diaphragm is provided. Since the conditional electronic circuit is distanced from the diaphragm, no interference between the conditional electronic circuit and the diaphragm occurs. Further, in the typical example of Patent Literature 2, a specific arrangement for electrically connecting the conditional electronic circuit and the sensing device terminal is not disclosed.
Likewise, in the typical example of Patent Literature 3, the signal conditioning circuit is provided to the rigid substrate distanced from the diaphragm, and thus does not interfere with the diaphragm. Further, in the typical example of Patent Literature 3, a specific arrangement for electrically connecting the connector terminal and the signal conditioning circuit is also not disclosed.